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Newt Gingrich, left, and Donald Trump. Donald Trump said it was "inappropriate" for Newt Gingrich to demand he drop the subject of an American judge's ethnicity and start acting like "a potential leader of the United States."

Donald Trump said Monday it was "inappropriate" for Newt Gingrich to demand he drop the subject of an American judge's ethnicity and start acting like "a potential leader of the United States."

But Trump let stand widespread scolding from other Republican leaders who want him to lay off the jurist — a sign that the GOP presidential candidate doesn't want to blow up the fragile truce he has struck with the party establishment.

Trump insisted that his comments about the judge came in defense against relentless questions from reporters and others about lawsuits against Trump University. Trump said U.S. District Court Judge Gonzalo Curiel can't be impartial in the suits because his parents were born in Mexico and Trump wants to build a wall along the border.

Curiel is a former federal prosecutor who was born in Indiana to parents who came from Mexico in the 1920s. He has not responded to Trump's attack, and Trump's legal team has not sought his removal from the case. Judges generally are thought to have conflicts of interest only in more specific situations, such as a financial interest in the outcome of the case.

Nonetheless, Trump says the public discussion about Trump University requires a response.

"All I'm trying to do is figure out why I'm being treated so unfairly by a judge," Trump said Monday on Fox News Channel.

Trump University is the target of two lawsuits — in San Diego and New York — which accuse the business of fleecing students with unfulfilled promises to teach secrets of success in real estate. Trump has maintained that customers were overwhelmingly satisfied.

A day earlier, Gingrich said Trump's focus on Curiel's ethnic background was "inexcusable" and Trump's "worst mistake." He was one of several Republicans who publicly demanded that the presumptive GOP candidate move on and unite the party.

Across the Sunday talk shows, Senate Majority Leader Mitch McConnell said that he "couldn't disagree more" with Trump's statements about Curiel's impartiality, adding that "we're all behind him now" — an implicit warning that such unity might not be the case for long.

Senate Foreign Relations Committee Chairman Bob Corker said he doesn't condone Trump's statements about Curiel, then complained that his interview was supposed to be about foreign policy.

"Attacking judges based on their race &/or religion is another tactic that divides our country. More importantly, it is flat out wrong," Kasich wrote.

Their remarks solidify the line GOP leaders have drawn in recent days between themselves and Trump, with whom they've made a fragile peace over their shared sense that almost anyone would be a better president than Democrat Hillary Clinton.

"I'm not changing," he said Tuesday at a fiery news conference at Trump Tower.

On Sunday, Trump doubled down on the idea. Asked on CBS whether a Muslim judge would be unfair given Trump's plan to ban Muslims from the U.S, Trump responded: "Yeah. That would be possible, absolutely."

That puts Trump in significant conflict with the Republicans he hopes to lead — including many who have opted to support him.

"I think it's a big mistake for our party to write off Latino Americans," said McConnell, a Republican from Kentucky.

Like Ryan, all of the Republicans delivering the move-on message to Trump have endorsed him. But their comments carried the implicit caveat that their support depends at least in part on Trump dropping his criticism of Curiel. All three also suggested ways Trump could move beyond his legal issues.